Gravitational Force & Energy Conservation

[Miraj Kayastha]

When Earth pulls a mass with gravitational force why does the energy of the earth-mass system decrease?
Isn't work just transfer of energy meaning constant overall energy?

 

[dauto]

Yes, the energy is transferred from Potential energy (which decreases as stated) to Kinetic energy. The two statements are not contradictory

 

[AZNathanielC]

The amount of energy in a closed system stays constant, it's just transferred into different forms. As dauto said, the energy is transferred to kinetic energy, although the total amount of energy stays constant within the system.

 

[Miraj Kayastha]

Then what does negative potential mean?

 

[Miraj Kayastha]

Why will an object lose energy when external force does negative work on it?

 

[jbriggs444]

Then what does negative potential mean?

It means that positive work would be required to move a unit mass from there to a position which is defined to have zero potential. If, for instance, you've defined the zero point to be at ground level then it means that you are in a hole. You would have to expend energy to climb out.

 

[Drakkith]

Why will an object lose energy when external force does negative work on it?

Here's how I understand it:

In the context of classical mechanics as you describe, negative work is performed by a force on an object roughly whenever the motion of the object is in the opposite direction as the force. This "opposition" is what causes the negative sign in the work. Such a negative work indicates that the force is tending to slow the object down i.e. decrease its kinetic energy.

From: http://physics.stackexchange.com/questions/65813/conceptually-what-is-negative-work